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Mark Wexler, Patrick Cavanagh; Fast motion drags shape. Journal of Vision 2019;19(10):288c. doi: https://doi.org/10.1167/19.10.288c.
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© ARVO (1962-2015); The Authors (2016-present)
Fast motion on the retina causes salient visual smear. At moderate speeds, this smear is suppressed when the motion lasts 30 ms or more (Burr, 1981). In contrast, smear from motion at saccadic speeds of several hundred degrees per second is not diminished at any duration. It is suppressed, however, if the motion is preceded by a static image of the moving object at the starting point and then finishes with a static image at the endpoint. The static endpoints create a paradoxical perception of a clear, moving object, but moving so fast that no clear shape should be seen. We examined whether this percept arises from de-smearing the actual moving shape, or whether it is an interpolation of the static endpoints. Observers discriminated between two shapes that moved over 10 deg at 200 deg/s (on a display refreshed at 1440 Hz). Without the static endpoints the shapes could be discriminated with near-perfect accuracy. We then displayed one of the shapes statically at the start and then at the end of the trajectory. The moving shape could be the same as the static shapes or not. When the duration of the static endpoints was over 50 ms, observers could no longer identify the moving shape. Instead, they reported that the clear moving shape was the shape of the static endpoints. We argue that the effect is distinct from apparent motion, and is not due to weighted averaging between the static and moving shapes. The effect breaks down for lower speeds, or motion that is sampled below 200 Hz. We conclude that fast, smooth motion can drag the percept of a briefly shown static shape along the motion path. This effect has obvious parallels to saccadic suppression and may explain why we perceive a clear world during saccades.
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